A spheroidal probe theory for a low‐density continuum plasma, i.e., one where the electron density is Ne ≲108 cm−3 and the gas pressure is P≳1 Torr has been developed using a spheroidal coordinate system in order to properly take into account the effect of the finite length of the probe. The numerical results of both the electron‐ and the ion‐current characteristics are obtained for various values of Rp/λD ranging from 0 to 1, ε = Ti/Te from 0.1 to 1, and Cp = Lp/2Rp from 1 to 100, where λD is the Debye length, Rp and Lp are the probe radius and the probe length, Ti and Te are the ion and the electron temperature, respectively. Using these results, new methods to determine the electron temperature and the plasma space potential (consequently, the electron density) by practical measurements are also proposed and discussed.